This invention relates to processes and products for effecting laser-induced thermal transfer imaging. More specifically, the invention relates to a modified thermally imageable element and its use in adjusting the focus of the imaging laser for imaging thermally imageable elements which are useful in color filters and liquid crystal display devices.
Liquid crystal display (LCD) devices have become increasingly important in displays which require very low consumption of electrical power or where the environment dictates a lightweight, planar, flat surface. For example, LCDs are used in display devices such as wristwatches, pocket and personal computers, and aircraft cockpit displays. When there is a need to incorporate a color display capability into such display devices, a component called a color filter is used. For the device to have color capability, each pixel is aligned with a color area, typically red, green, or blue, of a color filter array. Depending upon the image to be displayed, one or more of the pixel electrodes is energized during display operation to allow full light, no light, or partial light to be transmitted through the color filter area associated with that pixel. The image perceived by a user is a blend of colors formed by the transmission of light through adjacent color filter areas.
A major contributor to the cost of color LCD devices is the color filter. Four color filter manufacturing methods are known in the art, viz., dye gelatin, pigmented photoresist, electrodeposition and printing. The pigmented photoresist method offers the best trade-off of degradation resistance, optical properties, and flexibility along with high resolution, and is generally preferred. While conventional photolithographic materials and methods may be employed in the photoresist method, it suffers from the high cost and inconvenience associated with numerous process steps, some involving wet chemistry.
Laser-induced thermal transfer processes are well known in applications such as color proofing, electronic circuits, color filters, liquid crystal display devices, and lithography. Such laser-induced processes include, for example, dye sublimation, dye transfer, melt transfer, and ablative material transfer.
Laser-induced processes use a laserable assemblage comprising (a) a thermally imageable element that contains a thermally imageable layer, the exposed areas of which are transferred, and (b) a receiver element having an image receiving layer that is in contact with the thermally imageable layer. The laserable assemblage is imagewise exposed by a laser, usually an infrared laser, resulting in transfer of exposed areas of the thermally imageable layer from the thermally imageable element to the receiver element. The (imagewise) exposure takes place only in a small, selected region of the laserable assemblage at one time, so that transfer of material from the thermally imageable element to the receiver element can be built up one region at a time. The region may be a pixel, some portion of a pixel, or a number of pixels. Computer control produces transfer with high resolution and at high speed.
The equipment used to image thermally imageable elements is comprised of an imaging laser, and a non-imaging laser, wherein the non-imaging laser has a light detector that is in communication with the imaging laser. Since the imaging and non-imaging lasers have emissions at different wavelengths, problems occur with the proper focus of the imaging laser.
A need exists for a process for adjusting the focus of the imaging laser for imaging a thermally imageable element.
The invention provides a thermal imaging process that uses modified thermally imageable elements that improve the adjusting of the focus of an imaging laser in imaging thermally imageable elements. The invention greatly modifies the imaging latitude of the thermally imageable element by facilitating laser focus and imaging from color to color.